Molecular rotational spectroscopy is a technique that offers high chemical selectivity and sensitivity and can be used to analyze mixtures of gas samples. The technique is applicable to volatile species (e.g., having a minimum vapor pressure of about 0.1 Pascal (Pa)). Molecular rotational spectroscopy generally relies on a polar conformation of a molecule for detection (i.e., the molecule has a non-zero dipole moment). For room-temperature samples, a peak of the spectral intensity of a rotational spectrum typically occurs in the range of millimeter-wave (“mm-wave”) frequencies (e.g., from about 200 Gigahertz (GHz) to about 1000 GHz), particularly for molecules with 2-10 “heavy” nuclei (non-hydrogen atoms). A molecular rotational spectrum of most molecules will contain multiple, spectrally narrow transitions in any fixed mm-wave frequency range of modest bandwidth (e.g., a bandwidth of about 30 to about 50 GHz). Accordingly, a chemical analysis of a multiple component gas mixture can be made using a single mm-wave frequency range because all species will have spectroscopic transitions in the measurement range. However, the presence of overlapping spectra presents challenges to identifying the rotational spectrum of a single gas mixture component.